YK-11 (myostatin-related, not a true SARM)
YK-11 is a synthetic steroidal compound often grouped with SARMs but structurally a steroid derived from DHT. Its main proposed action is inhibition of myostatin signalling via follistatin, based only on cell-culture work. There is no human data; all effects and risks are preclinical or anecdotal, and it carries steroid-like suppression and possible hepatotoxicity.
01 Overview
YK-11 is a 5-alpha-reduced steroidal molecule that acts as a partial androgen-receptor agonist and, in myoblast cell studies, increases follistatin and thereby antagonises myostatin, the negative regulator of muscle growth. This myostatin angle drives its recreational appeal.
Because it is a steroid rather than a classic non-steroidal SARM, its safety profile is expected to resemble oral steroids more than mild SARMs, including suppression and potential liver strain. No clinical trials exist; dosing is entirely anecdotal and the compound is prohibited in sport and unapproved as a medicine.
02 Mechanism
Steroidal partial androgen-receptor agonist; in vitro it raises follistatin expression, inhibiting myostatin and potentially promoting muscle growth.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Light | 5–10 mg/day | Oral | Anecdotal only; no validated dose exists. |
| Common | 10–15 mg/day | Oral | Higher anecdotal range; risks poorly characterised. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Myostatin inhibition via follistatinCell-culture studies show increased follistatin and muscle-cell differentiation; not shown in living humans. | Preclinical | ||
| Increased muscle massUsers report size and fullness gains; entirely uncontrolled data. | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Joint and tendon discomfortSome users report dry or achy joints; mechanism unclear and unverified. | Mild | Uncommon | Anecdotal | |
| Testosterone suppressionAs a steroidal androgen-receptor agonist, YK-11 is expected to suppress endogenous testosterone. | Moderate | Common | Anecdotal | |
| Possible hepatotoxicityBeing a steroidal compound, liver strain is plausible; no human data confirm or quantify risk. | Moderate | Unknown | Anecdotal |
06 Commonly used with
What yk-11 is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Stacked compounds | ||
| Testolonestrength | Paired with testolone in short, aggressive strength or recomp blocks where YK-11's myostatin-related mechanism is meant to add fullness.Trade-off: Stacking two suppressive, poorly-characterised compounds compounds hormonal shutdown and unknown long-term risk. | |
| Ostarinerecomp | Ostarine is used as a milder base so YK-11 can be run at a low dose for a recomp rather than alone.Trade-off: YK-11 is often described as a steroidal compound rather than a true SARM, and combining it still deepens suppression with little human data behind it. | |
| Support & ancillaries | ||
| TestosteroneTRT base | A TRT-dose testosterone base is sometimes added to maintain androgenic function given YK-11's suppression.Trade-off: It turns the cycle into an injectable steroid protocol with aromatisation and cardiovascular considerations layered onto an already unproven compound. | |
| Post-cycle | ||
| TamoxifenPCT | YK-11 is suppressive, so users typically run a SERM PCT afterward to help natural testosterone rebound.Trade-off: Human safety data on YK-11 is essentially absent, and a SERM cannot compensate for risks that have never been studied. | |